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This might seem like a naive question to ask! But... I know how a turbo charger works and (since I bought my MCS a couple of months ago) I also know how a supercharger works. The pressure with a turbo varies according to whether its spinning or not - is it therefore true that a supercharger will always produce the same amount of pressure because it's always spinning?

Part of the reason for asking this is that I'm thinking of fitting additional gauges and the thought of a boost pressure gauge which never moves bores my to tears...!

Mini Mod

This might seem like a naive question to ask! But... I know how a turbo charger works and (since I bought my MCS a couple of months ago) I also know how a supercharger works. The pressure with a turbo varies according to whether its spinning or not - is it therefore true that a supercharger will always produce the same amount of pressure because it's always spinning?

Part of the reason for asking this is that I'm thinking of fitting additional gauges and the thought of a boost pressure gauge which never moves bores my to tears...!

BMW Traitor

supercharger and turbos both achieve max boost at high rpms. superchargers work better than turbos at low revs due to the lack of exhaust pressure. turbos become more efficient at high revs than superchargers because they don't "eat" the energy from the engine.

to make it short, boost isn't always the same, vary the rpms and you can see the boost go up and down.

Brrrp Brrrp!!!

supercharger and turbos both achieve max boost at high rpms. superchargers work better than turbos at low revs due to the lack of exhaust pressure. turbos become more efficient at high revs than superchargers because they don't "eat" the energy from the engine.

to make it short, boost isn't always the same, vary the rpms and you can see the boost go up and down.

So is this to say that for the Cooper S, the boost will kick in till the next gear change? Or to re-phase, there isn't a cut off point for the super charger as oppose to the turbo charger where it'd only spool in at, say 4000 revs.

Mini Mod

So is this to say that for the Cooper S, the boost will kick in till the next gear change? Or to re-phase, there isn't a cut off point for the super charger as oppose to the turbo charger where it'd only spool in at, say 4000 revs.

Depends on the turbo or the supercharger. It's all in the design. But basically you select a supercharger that will give you the most efficient boost at the correct RPM. You can't overboost with a properly selected SC.

Not a turbo guy but design plays a part here too. You can get a turbo to spool in earlier but generally that's because the impeller itself is smaller and lighter. The downside it it could fade in the upper RPM range. Reverse that for bigger turbos.
That's what's behind the current trend and why everyone thinks the whole pop off valve squeek is so cool. Big boost....I must be fast.......... Faster......yes. Fast...maybe.
Don't get me wrong. Turbos are awesome but on many car they're just like fart pipes. A lot of noise and not much performance.
And yes the same can be said for an SC that's too big or too small.
I raced against a guy years ago that stuck a big blower on his crap small block car. I beat him badly with my basically stock daily driver. He was stunned. I had more money

Read the link I posted above to help get a handle on how the bypass valve works in an Eaton blower.

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Apply a little logic here. People are always talking about boosting their engine power with a new supercharger pulley. The reduced size means that it turns faster than the stock when driven by the same size drive pulley, so it produces more "boost." A supercharger is run from the engine crankshaft or some other shaft. A turbocharger is run by the exhaust gases. The higher the rpm of the supercharger or turbocharger, the more "boost" exists.

The engine manages the boost with a "waste gate" where it can vent excess pressure if it is not needed, so the engine can always REDUCE the boost at any given RPM. With both turbo and supercharger, the boost decreases as engine RPM decreases, but the supercharger, which is exactly fixed to engine rpm by the pulley will drop off with a different curve than the turbo run by the exhaust gases.

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BTW, some clarification. Boost changes A LOT while driving. You will only see peak boost for a given RPM at WOT (wide open throttle). The vast majority of the time (99% ?) the engine is under vacuum, so boost is less than 0 psi? So, a boost gauge moves quite a bit and is just as interesting to watch in a supercharged car as it is in a turbo. It is not accurate to say that boost always climbs or always falls as revs climb. My last 2 cars had completely different boost behavior:

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